Choosing the Right Wall Assembly

Interstitial condensation during cold months on the first condensing surface in the assembly is always a function of interior relative humidity, as well as the temperature profile of the assembly. Let’s not forget to manage wintertime interior relative humidity as we manage the assembly profile. A continuous air barrier is critical no matter which assembly is selected; interstitial condensation driven by air leakage trumps vapor drive by a long shot. Look at the wetting and the drying. The famous Canadian building scientist, Mark Bomberg, is known for, among many things, this quote: “Our buildings get wet during the winter but don’t rot till the summer.” He was speaking in the context of adding central air conditioning to homes in cold climates; without the AC they were getting wet in the winter and drying out in the summer. Add AC, and the reduced drying sends the assembl...